1. Field of the Invention
The present invention relates to a thin-film magnetic head having at least an induction-type electromagnetic transducer, and a method of manufacturing same.
2. Description of the Related Art
Recent years have seen significant improvements in the areal recording density of hard disk drives. In particular, areal recording densities of latest hard disk drives reach 80 to 100 GB/platter and are even on a pace to exceed that level. Thin-film magnetic heads are required of improved performance accordingly.
Among the thin-film magnetic heads, widely used are composite thin-film magnetic heads made of a layered structure including a recording head having an induction-type electromagnetic transducer for writing and a reproducing head having a magnetoresistive element (that may be hereinafter called an MR element) for reading.
In general, a recording head incorporates: a medium facing surface (air bearing surface) that faces toward a recording medium; a bottom pole layer and a top pole layer that are magnetically coupled to each other and include magnetic pole portions opposed to each other and located in regions of the pole layers on a side of the medium facing surface; a recording gap layer provided between the magnetic pole portions of the top and bottom pole layers; and a thin-film coil at least part of which is disposed between the top and bottom pole layers and insulated from the top and bottom pole layers. In the typical recording head, the bottom pole layer and the top pole layer are magnetically coupled to each other via a coupling portion which is located away from the medium facing surface. The thin-film coil has the shape of a flat spiral, and is disposed around the coupling portion.
Higher track densities on a recording medium are essential to enhancing the recording density among the performances of a recording head. To achieve this, it is required to implement a recording head of a narrow track structure in which the track width, that is, the width of the two magnetic pole portions opposed to each other on a side of the medium facing surface, with the recording gap layer disposed in between, is reduced down to microns or the order of submicron. Semiconductor process techniques are utilized to achieve such a structure.
As the track width decreases, it becomes harder to generate a high-density magnetic flux between the two magnetic pole portions that are opposed to each other with the recording gap layer in between. On that account, it is desirable that the magnetic pole portions be made of a magnetic material having a higher saturation flux density.
When the frequency of the recording signal is raised to increase the recording density, recording heads require an improvement in the speed of change of flux, or equivalently, a reduction in flux rise time. The recording heads also require less degradation in such recording characteristics as an overwrite property and non-linear transition shift at high frequency bands. For improved recording characteristics at high frequency bands, the magnetic path length is preferably made smaller. The magnetic path length is determined chiefly by the length of a portion of the bottom or top pole layer, the portion lying between the coupling portion and the medium facing surface (referred to as yoke length in the present application). A reduction in yoke length is effective at reducing the magnetic path length. The yoke length is effectively reduced by decreasing the winding pitch of the thin-film coil, or the pitch of a portion of the winding which lies between the coupling portion and the medium facing surface, in particular.
One of known techniques for decreasing the winding pitch of a thin-film coil is to form a recess in the bottom pole layer so as to place the thin-film coil in the recess (see the specification of U.S. Pat. No. 6,043,959).
According to the method of manufacturing a thin-film magnetic head described in U.S. Pat. No. 6,043,959, the bottom pole layer, the top pole layer, and the thin-film coil are formed through the following steps. Initially, the bottom pole layer patterned into a predetermined shape is formed. A recording gap layer and a magnetic layer are then formed on the bottom pole layer in succession. Part of the magnetic layer is coupled to the bottom pole layer. Then, a mask is formed to cover portions of the magnetic layer where to form the magnetic pole portion of the top pole layer and where to form the coupling portion. The magnetic layer, the recording gap layer and the bottom pole layer are etched by using this mask. Consequently, the magnetic layer after the etching makes a pole portion layer that is to be the magnetic pole portion of the top pole layer, and a coupling layer that is to be the coupling portion. The above-mentioned etching also forms a trim structure, in which the magnetic pole portion of the top pole layer, the recording gap layer, and part of the bottom pole layer make vertical, self-aligned sidewalls. The etching also provides the bottom pole layer with a recess in which the thin-film coil is to be placed. An insulating film is then formed all over, and thereafter, the thin-film coil is formed by plating on the insulating film inside the recess. Then, a thick insulating layer is formed all over and the top surface of this insulating layer is flattened to expose the pole portion layer and the coupling layer of the top pole layer. On the flattened surface, a yoke portion layer of the top pole layer is formed so that the pole portion layer and the coupling layer are coupled to each other.
In the thin-film magnetic head described in U.S. Pat. No. 6,043,959, an end of the coupling portion closer to the medium facing surface has a part that extends linearly in parallel with the medium facing surface.
Another known technique for decreasing the winding pitch of the thin-film coil is to arrange the winding of a second coil in a winding gap of a first coil (see the specification of U.S. Pat. No. 6,191,916 B1).
U.S. Pat. No. 5,995,342 describes a planar head having flat coils of three turns. This head has a magnetic core frame which comprises a single bottom pole layer, two plate-shaped struts connected to respective ends of the bottom pole layer, and two top pole layers connected to the respective struts. The struts are shaped like a plate and are arranged perpendicular to the bottom pole layer and the top pole layers. The flat coils are disposed respectively around the struts.
In the thin-film magnetic head described in U.S. Pat. No. 6,043,959, the end of the coupling portion closer to the medium facing surface has the part that extends linearly in parallel with the medium facing surface. In this thin-film magnetic head, the thin-film coil has a plurality of conductor portions (hereinafter referred to as linear conductor portions) arranged between the coupling portion and the medium facing surface. The linear conductor portions extend linearly in parallel with the medium facing surface. To reduce the yoke length of this thin-film magnetic head, the linear conductor portions must be made smaller in width. The longer the linear conductor portions are, the higher the resistance of the entire thin-film coil becomes. The shorter the linear conductor portions, the lower the resistance of the entire thin-film coil.
As described above, thin-film magnetic heads desirably have smaller yoke lengths for the sake of improved recording characteristics at high frequency bands. It is therefore effective to reduce the pitch of the portion of the thin-film coil winding which lies between the coupling portion and the medium facing surface. In conventional thin-film magnetic heads however, a reduction in the above-mentioned pitch can decrease the width of the linear conductor portions and thus increase the resistance of the linear conductor portions. Since the conventional thin-film magnetic heads have linear conductor portions of relatively greater lengths, the resistance of the linear conductor portions occupies a considerable portion of the resistance of the entire thin-film coil, e.g., 60-70%. Under the circumstances, the conventional thin-film magnetic heads have had the problem that the thin-film coil increases in resistance when the yoke length is reduced to improve the recording characteristics at high frequency bands.
For improved recording characteristics of the thin-film magnetic heads, it is also desirable to increase the number of turns of the thin-film coil. Nevertheless, if the yoke length is reduced as described above and the number of turns of the thin-film coil is increased at the same time, the conventional thin-film magnetic heads become yet smaller in the width of the linear conductor portions, which results in further increases in the resistance of the linear conductor portions and the resistance of the entire thin-film coil.
As the resistance of the thin-film coil increases, there arises a problem that the magnetic pole portions can protrude toward the recording medium due to heat occurring from the thin-film coil and thus the magnetic pole portions become more likely to collide with the recording medium.
Thus, in the conventional thin-film magnetic heads it has been unfeasible to reduce the yoke length considerably from the viewpoint of avoiding the problem that occurs from an increase in the resistance of the thin-film coil.
As mentioned above, for the sake of improved recording characteristics of the thin-film magnetic heads, it is also desirable to increase the number of turns of the thin-film coil. In the conventional thin-film magnetic heads, however, the turns of winding of the thin-film coil increase in length of the linear conductor portions as the turns are closer to the outer periphery of the winding. Thus, when the number of turns of the thin-film coil is increased, the thin-film coil becomes greater in resistance as well as in the area which the thin-film coil occupies. The increase in the area makes it difficult to obtain smaller thin-film magnetic heads.
In the conventional thin-film magnetic heads, the width of the linear conductor portions must be reduced for the sake of a smaller yoke length. As the width of the linear conductor portions decreases, however, it becomes difficult to form the linear conductor portions with precision, as will be discussed later.
In general, the thin-film coil is formed by frame plating through the following steps. Initially, a photoresist frame is formed by photolithography. Then, a thin electrode film is formed to cover this frame. With an electric current passed through this electrode film, the thin-film coil is formed by electroplating. When the thin-film coil is to be formed in a recess of the bottom pole layer, the frame must be formed on the uneven bottom pole layer. When the frame is formed by photolithography on such an uneven base, rays of light used for exposure of photolithography are reflected off the electrode film lying on the sidewalls of the recess. The photoresist is exposed to the reflected rays as well. For that reason, it is difficult to form a fine frame precisely on an uneven base by photolithography.
Consequently, for example, if a thin-film coil having a thickness of 1.5 μm or more and having linear conductor portions of 0.3 μm or less in width or 0.5 μm or less in pitch is to be formed in the recess of the bottom pole layer by the existing photolithography techniques, the yield of the thin-film coil becomes extremely low, and therefore it is practically difficult to form such a coil.
The technology described in U.S. Pat. No. 6,191,916 B1 can be used to reduce the spacing between adjoining windings. The thin-film magnetic head described in U.S. Pat. No. 6,191,916 B1, however, has thin-film coils of constant winding widths. In this thin-film magnetic head, the thin-film coils can thus increase in resistance when the winding widths are reduced for the sake of a smaller yoke length.
In the planar head described in U.S. Pat. No. 5,995,342. the flat coils are disposed respectively around the plate-shaped struts. The flat coils each have a plurality of linear conductor portions which extend linearly in parallel with both surfaces of the struts. To reduce the yoke length of this planar head, the linear conductor portions must be reduced in width. Since the linear conductor portions in this planar head are relatively long, there is a problem that a reduction in the yoke length can cause an increase in the resistance of the thin-film coil.